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The urinary system does several functions
- 1. The Kidneys remove nitrogenous wastes:
- urea, uric acid, ammonia from the liver from the breakdown of proteins.
- Urea is the most abundant organic waste in urine.
- Creatinine is from the breakdown of a muscle energy molecule.
- 2. Acid/Base balance, stabilizes the body’s pH by excreting or retaining H + ions
- 3. Water balance, retains water for normal osmotic pressure and blood pressure.
- 4. Electrolyte balance of Na+, K+, Cl-, Ca +, Phosphate 5. Endocrine function-produces renin (turns to Angiotensin II in lungs), erythropoietin, and activates Vitamin D.
- 6. Retention of nutrients and removal of drugs and toxins.
The organs of the system include:
- 2 kidneys that produce the urine
- 2 ureters, one from each kidney that conducts the urine to the bladder.
- 1 bladder, stores the urine
- 1 urethra, conducts urine outside the body. (Memory aid – there is A single urethra)
Where are the kidneys located?
They are retroperitoneal, or behind the parietal side of the peritoneal membraneof the abdomen, between vertebrae T12- L3. The left kidney is slightly superior to the right.
is a granular area between the capsule and the medulla containing nephrons
is the inner striated region of collecting tubules forming renal pyramids whose apex istoward the calyx
The Renal column
The region between the medulla
The Major and minor Calyx
The Renal pelvis
- is the urine collecting funnel from calyx to the ureter that goes to the bladder.
- Smooth muscle of the ureter uses peristalsis to move urine to bladder.
The functional unit of the kidney
- The Nephrons
- lies in the cortex and the renal pyramids of the medulla. Each kidney has over 1 million nephrons.
Following the blood surrounding the typical nephron:
Coming off the descending aorta the renal artery eventually becomes the afferent arterioles that each deliver blood to one nephron which has glomerulus capillaries that are fenestrated and inside the Bowman’s Capsule, where blood is filtered and drains to efferent arterioles which become the peritubular capillaries, a web-work of vessels surrounding the nephron which eventuallydrains to the renal vein which drains in the inferior vena cava.
3 Different Processes involved in making urine
- 1. Filtration – the blood pressure forces much of the plasma, except the large proteins, across the glomerulus and into the Bowman’s capsule and this is the only place where filtration occurs.So materials, including nutrients move from IN the blood to OUT of the body (to tubule).
- 2. Reabsorption – is a selective process that may be due to osmosis, diffusion or carrier proteinsthat returns nutrients back to the blood from the nephron tubule to the surrounding capillaries.Different areas of the tubule have different reabsorptive abilities due to the different distributionof carrier proteins and solute concentrations. The PCT does the majority of the reabsorption.Materials move from OUT to IN the blood.
- 3. Secretion – is the transport of some solutes back into the nephron tubule to fine tune the urineand get out of the body H+, and various ionsMaterials move from IN to OUT of the body.
Renal corpuscle or the combined glomerulus and Bowman’s capsule
produce a filtrate due to the blood pressure or normal hydrostatic pressure of blood. The filtrate hassmall proteins, salts, glucose, free fatty acids, vitamins and water. The glomerulus continues asthe efferent arteriole that becomes the peritubular capillaries
Proximal convoluted tubule, PCT in cortex of the kidney = majority of the reabsorption
- Active transport (ATP) of glucose and amino acids, vitamins, ions and other materials.
- Glucose requires a carrier protein to be reabsorbed.
- Water is always moved by osmosis.
The loop of Henle is mostly in the medulla of the kidney
There is the descending Loop of Henle, where water is reabsorbed by osmosis andthe ascending Loop of Henle where Na+ and Cl-ions are reabsorbed.
The distal convoluted tubule, DCT, in the cortex of the kidney
- reabsorbs sodium exchanging it for K+, due to Aldosteronereabsorbs calcium ions from tubular fluid, due to PTH
- - reabsorbs water through aquaporins
- - responds to ADH and Aldosterone to reabsorb sodium and water and secrete K+
The collecting duct
- receives urine from several nephrons.
- -also responds to ADH and Aldosterone and reabsorbs water to concentrate urine.
There are two types of Nephrons
1. cortical nephrons – majority of all nephrons
2. juxtamedullary nephrons – have a long loop of Henle in the medullary portion of thekidney. These longer nephrons have a longer capillary system where, the peritubular capillariescontinue as the vasa recta capillaries. They make very concentrated the urine due to the saltyosmotic gradient of the medulla which creates a counter-current exchange between the loopof Henle and the vasa recta capillaries. The medulla allows reabsorption of water by osmosis.
Erythropoietin is produced when?
The Kidneys are Hypoxic
- the presence of protein in the urine is always abnormal.
- It may be due to cellularcasts which would indicate to kidney injury. Or it may be due to RBCs or WBCs
the presence of glucose in the urine that is often indicative of diabetes mellitus.
- is never reabsorbed and it always leaves the body in the glomerular filtrate.
- So if creatinine is high and the BUN is high, then the GFR is very low and the kidneys are failing.
an excess of Blood Urea Nitrogen in the blood, also called uremia
Acute Renal Failure
recent, rapid loss of blood filtering ability. It may be due to avariety of causes, diseases, drugs, toxins, etc. and it may not be permanent.
Chronic Renal Failure
- long term, slow loss of blood filtering ability. It may due to avariety of causes and it is a permanent disability. Dialysis maybe needed.
- Diabetes mellitus isprimary cause of CRF due to complications of hyperglycemia and hypertension.
Kidney Injuries – very active cells depending on blood for oxygen, nutrients, and removal ofwastes.
3 basic ways to injure the kidneys:
Pre-renal- a condition that has causes primary decreased blood pressure and secondarily decreases GFR and causes kidney failure.example: dehydration, hypotension due to heart failure
Renal – a condition that primarily damages the kidneys and causes kidney failure.example: glomerulonephritis, pyelonephritis, inflammation, toxins.
Post-renal – a condition that has secondarily caused kidney failure due to a primary problem of urine obstruction and subsequent back up into the nephrons.example: kidney stones, ureter tumors, prostate tumors.
Consequences of Kidney failure:
- 1. High nitrogenous wastes in plasma, High BUN, blood urea nitrogen, (azotemia) and creatinine.
- 2. Electrolyte imbalances, High K+ , H+ (acidosis) and Low Na+, Ca2+
- 3. Fluid imbalances
- 4. Treat underlying causes of CRF such as hypertension, Diabetes Mellitus, etc.
- smooth muscle called detrusor muscle surrounds bladder.
- Contraction of the detrusor muscle expels urine through the urethra.
Transitional cell epithelium lines the bladder mucosa and can flatten as bladder fills with urine
triangular funnel-shaped distal area, 2 exits of ureters & 1 entrance to the urethra,common area for bacteria to colonize, cancer to occur.
Internal/External Urethral Sphincters
- Internal Urethral Sphincter – involuntary control = smooth muscle
- External Urethral Sphincter – voluntary control
Spinal injury above the sacral plexus would cause...?
Spinal injury at the sacral plexus would cause...?